Hypothalamic temperature and osmoregulation in the Pekin duck

The temperature of the anterior and middle hypothalamus of conscious Pekin ducks was altered with chronically implanted thermodes. Both urine formation and salt secretion by the supraorbital glands were influenced by hypothalamic cooling. When osmotic diuresis was induced by continuous intravenous infusion of 1.2 ml·min^–1 of 293 mosm·kg^–1 mannitol in H₂O solution, hypothalamic cooling increased urine flow rate at reduced urine osmolality and unchanged osmolal excretion rate. The degree of this cold induced diuresis increased with cooling intensity. Additional ADH administration by continuous infusion at a supramaximal dose abolished the diuretic effect of hypothalamic cooling. When water diuresis was induced by intragastric continuous infusion of 1.2 ml·min^–1 of distilled water, hypothalamic cooling enhanced the diuresis, but hypothalamic warming had equivocal effects. The diuretic effects of hypothalamic cooling suggest an inhibition of endogeneous ADH release by lowering hypothalamic temperature. When the salt glands of salt adapted ducks were stimulated by continuous intravenous infusion of 0.2 ml·min^–1 of 800 mosm·kg^–1 NaCl in H₂O solution, hypothalamic cooling reduced the salt gland secretion rate to an extent depending on cooling intensity. It is concluded that the activities of those integrative and/or efferent hypothalamic neurons, which mediate the hormonal control of renal water absorption and the nervous control of salt secretion by the supraorbital gland, depend on their own temperature.Supported by Deutsche Forschungsgemeinschaft (Si 230/1)     

Effect of organic acid absorption on bicarbonate transport in rat colon

The absorption of organic anions and the influence of these anions on the movement of HCO ₃ ^– were studied in vivo in rat colon using a perfusion technique. The absorption of short chain fatty acids (SCFA's) such as acetate, propionate, and butyrate was much greater than that of succinate or lactate. With increasing initial concentration of SCFA up to 100 mmol · l^–1, SCFA absorption increased linearly in correspondence with HCO ₃ ^– appearance. FinalpCO₂ level of the perfusion solution with SCFA was the same as the plasma level. Among the SCFA's, no significant differences in absorption or their effects on HCO ₃ ^– appearance were observed. The presence of Na⁺ stimulated SCFA absorption, and the maximum value was obtained at more than 100 mmol · l^–1 of Na⁺.These results suggest that a specific system for HCO ₃ ^– secretion activated by SCFA exists in the colon, and that this system may control the intraluminal pH by the alkalization of intestinal contents.     

Effects of dichloroacetate on exercise performance in healthy volunteers

Dichloroacetate (DCA), a stimulator of the pyruvate dehydrogenase complex, decreases lactate levels and peripheral resistance and increases cardiac output. This study was performed to examine the effects of DCA on exercise performance in humans. Eight healthy male volunteers (age 20–28 years) were tested by bicycle spiro-ergometry using a microprocessor-controlled gas analysis system after infusion of DCA (50 mg/kg body weight) or saline. Prior infusion of DCA significantly reduced the increase of lactate levels during exercise when compared with infusion of saline (1.40±0.21 vs 2.10±0.09 mmol·l^–1 at 50% of the expected maximal working capacity, P<0.05; 8.53±0.45 vs 9.92±0.59 mmol·l^–1 at maximal working capacity, P<0.05). Oxygen uptake increased significantly after DCA when compared with saline from 7.5±0.4 vs 7.4±0.5 to 27.2±1.5 vs 23.7±1.7 (P<0.05) at anaerobic threshold and to 35.6±1.7 vs 30.5±1.0 ml · kg^–1 min^–1 (P<0.05) at maximal exercise capacity. Following DCA infusion the workload at which the anaerobic threshold was reached was significantly higher (160±7 vs 120±5 W, P<0.05) and the maximal working capacity was significantly increased (230±9 vs 209±8 W, P<0.05). In summary, DCA reduced the increase of lactate levels during exercise and increased oxygen uptake at the anaerobic threshold and at maximal working capacity, which was significantly increased. These results warrant further studies on a potential therapeutic application of DCA in patients with reduced exercise capacity.     

Scaling physiological measurements for individuals of different body size

Summary This paper examines how selected physiological performance variables, such as maximal oxygen uptake, strength and power, might best be scaled for subject differences in body size. The apparent dilemma between using either ratio standards or a linear adjustment method to scale was investigated by considering how maximal oxygen uptake (1·min^–1), peak and mean power output (W) might best be adjusted for differences in body mass (kg). A curvilinear power function model was shown to be theoretically, physiologically and empirically superior to the linear models. Based on the fitted power functions, the best method of scaling maximum oxygen uptake, peak and mean power output, required these variables to be divided by body mass, recorded in the units kg^2/3. Hence, the power function ratio standards (ml·kg^–2/3·min^–1) and (W·kg^–2/3) were best able to describe a wide range of subjects in terms of their physiological capacity, i.e. their ability to utilise oxygen or record power maximally, independent of body size. The simple ratio standards (ml·kg^–1·min^–1) and (W·kg^–1) were found to best describe the same subjects according to their performance capacities or ability to run which are highly dependent on body size. The appropriate model to explain the experimental design effects on such ratio standards was shown to be log-normal rather than normal. Simply by taking logarithms of the power function ratio standard, identical solutions for the design effects are obtained using either ANOVA or, by taking the unscaled physiological variable as the dependent variable and the body size variable as the covariate, ANCOVA methods.     

The energy cost of walking or running on sand

Summary Oxygen uptake ( O₂) at steady state, heart rate and perceived exertion were determined on nine subjects (six men and three women) while walking (3–7 km · h^–1) or running (7–14 km · h^–1) on sand or on a firm surface. The women performed the walking tests only. The energy cost of locomotion per unit of distance (C) was then calculated from the ratio of O₂ to speed and expressed in J · kg^–1 · m^–1 assuming an energy equivalent of 20.9 J · ml O₂ ^–1. At the highest speedsC was adjusted for the measured lactate contribution (which ranged from approximately 2% to approximately 11% of the total). It was found that, when walking on sand,C increased linearly with speed from 3.1 J · kg^–1 · m^–1 at 3 km · h^–1 to 5.5 J · kg^–1 · m^–1 at 7 km · h^–1, whereas on a firm surfaceC attained a minimum of 2.3 J · kg^–1 · m^–1 at 4.5 km · h^–1 being greater at lower or higher speeds. On average, when walking at speeds greater than 3 km · h^–1,C was about 1.8 times greater on sand than on compact terrain. When running on sandC was approximately independent of the speed, amounting to 5.3 J · kg^–1 · m^–1, i.e. about 1.2 times greater than on compact terrain. These findings could be attributed to a reduced recovery of potential and kinetic energy at each stride when walking on sand (approximately 45% to be compared to approximately 65% on a firm surface) and to a reduced recovery of elastic energy when running on sand.     

Plasma testosterone and catecholamine responses to physical exercise of different intensities in men

Summary Plasma testosterone, noradrenaline, and adrenaline concentrations during three bicycle ergometer tests of the same total work output (2160 J·kg^–1) but different intensity and duration were measured in healthy male subjects. Tests A and B consisted of three consecutive exercise bouts, lasting 6 min each, of either increasing (1.5, 2.0, 2.5 W·kg^–1) or constant (2.0, 2.0, 2.0 W·kg^–1) work loads, respectively. In test C the subjects performed two exercise bouts each lasting 4.5 min, with work loads of 4.0 W·kg^–1. All the exercise bouts were separated by 1-min periods of rest.Exercise B of constant low intensity resulted only in a small increase in plasma noradrenaline concentration. Exercise A of graded intensity caused an increase in both catecholamine levels, whereas, during the most intensive exercise C, significant elevations in plasma noradrenaline, adrenaline and testosterone concentrations occurred. A significant positive correlation was obtained between the mean value of plasma testosterone and that of adrenaline as well as noradrenaline during exercise.It is concluded that both plasma testosterone and catecholamine responses to physical effort depend more on work intensity than on work duration or total work output.This work was performed within the Scientific Exchange Programme between the Institute of Experimental Endocrinology, Slovak Academy of Sciences in Bratislava and Medical Research Centre, Polish Academy of Sciences, Warsaw/Project 10.4/     

The role of the cardiac nerves in the regulation of sodium excretion in conscious dogs

Conscious, chronically instrumented dogs, maintained on a high sodium intake, were used to investigate whether surgical cardiac denervation impairs the natriuresis associated with left atrial pressure increase produced in three ways: during an increase in left atrial pressure by means of a reversible mitral stenosis (protocol 1); after an i.v. saline load (1.0 ml 0.9%·saline min^–1·kg^–1 over 60 min) (protocol 2); after an oral saline load (14.5 mmol Na·kg^–1 given with the food as an isotonic solution) (protocol 3).During a reversible mitral stenosis, in intact dogs, urine volume and sodium excretion increased markedly (from 34–145 l·min^–1·kg^–1 and from 3–12 mol·min^–1·kg^–1); mean arterial pressure increased by an average of 2 kPa (15 mm Hg) and heart rate by 55 b/min; plasma renin activity fell from 0.37–0.21 ng Al·ml^–1·h^–1. Cardiac denervation eliminated these effects of left atrial distension except for a small increase in heart rate (12 b/min). This indicates that the natriuresis and diuresis during left atrial distension resulted from stimulation of receptors located in the left atrium.In contrast, during protocol 2 and 3, the same amounts of sodium and water were excreted in the cardiac denervated dogs as compared to the intact dogs. A comparable decrease in plasma renin activity also was observed. — Apparently the presence of the cardiac nerves is not a prerequisite for maintenance of sodium and water homeostasis.     

Athletes' pseudoanaemia

Summary To characterize the so-called pseudoanaemia of endurance-trained athletes, the plasma volume (PV), red cell volume (RCV) and total blood volume (TBV) of 12 male and 12 female athletes and 5 male and 5 female nonexercising controls were measured using¹²⁵I-la-belled human serum albumin and⁵¹Cr-labelled erythrocytes. The mean PV of the male athletes (52.8 ml·kg^–1) was 37.5% higher than that of the controls (38.4 ml·kg^–1), while the 18.1% increase measured in the female runners (51.5 ml·kg^–1) over the controls (43.6 ml·kg^–1) was a novel observation. Although the RCV was significantly greater (34.7%) in male athletes (32.6 ml·kg^–1 vs 24.2 ml·kg^–1 in the controls), a similar elevation (3.6%) was not found in the female athletes (25.9 ml·kg^–1) compared to the sedentary women (22.8 ml·kg^–1). This could have been due to iron-limited erythropoiesis because the RCV of the female athletes defined as clinically anaemic was markedly lower that of the nonanaemic women (P<0.05). The elevated plasma protein mass and concentration measured in the athletes partly accounted for their expanded PV. It was concluded that the decreased blood haemoglobin levels reported in the endurance athletes was largely a dilutional effect.     

Verification of the heart rate threshold

Among the methods for determining anaerobic threshold (AT), the heart rate (HR) method seems to be the simplest. On the other hand, many conflicting results from comparing this method with others have been presented over the last 10 years. Therefore, the aim of this study was to compare the heart rate threshold (HRT) with the lactate turn point (LTP) —second break point of dependence of lactate (LA) to power output, ventilatory threshold (VT) and threshold determined by electromyography (EMG_AT), all determined by the same exercise test and evaluated by the same computer algorithm. A group of 24 female students [mean age 20.5 (SD 1.6) years, maximal oxygen consumption 48.8 (SD 4.7) ml · kg^–1 · min^–1 performed an incremental exercise test on a cycle ergometer (modified Conconi test) starting with an initial power output (PO) of 40 W with intensity increments of 10 W · min^–1 until the subjects were exhausted. The HRT, LTP and EMG_AT determination was done by computer-aided break-point regression analysis from dependence of functional measures on PO. The same computer algorithm was used for VT determination from the relationship between ventilation (V) and oxygen uptake ( O₂) or carbon dioxide output ( CO₂). Nonsignificant differences were found between HRT [ O₂ 35.2 (SD 4.2) ml · kg^–1 · min^–1; HR 170.8 (SD 5.5) beats min^–1; LA 4.01 (SD 1.03) mmol · l^–1; PO 2.27 (SD 0.33) W · kg^–1 VT [ O₂ 35.1 (SD 3.7) ml · kg^–1 · min^–1 HR 168.3 (SD 4.8) beats · min^–1; LA 3.87 (SD 1:17) mmol · l^–1; PO 2.22 (SD 0.27) W · kg^–1 EMG_AT [ O₂35.6 (SD 4.1) ml · kg^–1 · min^–1 HR 171.0 (SD 5.4) beats · min^–1; LA 4.11 (SD 0.98) mmol · l^–1; PO 2.30 (SD 0.31) W · kg^–1] and LTP [ O₂) 35.3 (SD 4.1) ml · kg^–1 · min^–1; HR 170.1 (SD 6.0) beats · min^–1; LA 3.99 (SD 0.76) mmol · l^–1; PO 2.27 (SD 0.29) W · kg^–1]. Highly significant correlations (P < 0.01 in all cases) were found among all measurements made at threshold level in all the thresholds investigated. Correlation coefficients ranged in selected variables at different threshold levels from 0.842 to 0.872 in O₂ measured in ml · kg^–1 · min^–1, from 0.784 to 0.912 for LA, from 0.648 to 0.857 for HR, and from 0.895 to 0.936 for PO measured in W · kg^–1. These findings have led us to conclude that HRT could be used as an alternative method of determining anaerobic threshold in untrained subjects.     

Metabolic cost of exercise and physical performance in children with some observations on external loading

Summary The metabolic cost (VO₂) of running was studied on a motor-driven treadmill in nine athletic boys, five athletic girls, and nine active boys aged 11–13 years and the results compared with their performance times during racing out of doors. On 15 of the children, additional observations of the effects of external loading on aerobic power output were made. The results showed that VO₂ was proportional to body weight in children but when expressed in ml·kg^–1·min^–1, VO₂ for a given speed of running was significantly higher in children than expected from previously collected data on adults. There were no significant differences between aerobic cost of running of the athletic boys, girls, or the active boys. The increased VO₂ ml·kg^–1·min^–1 in children appeared to be independent of stride length and frequency but external loading equivalent to 5% of body weight reduced VO₂ (ml·kg^–1·min^–1), particularly at the higher speeds. It was suggested in young active and athletic children due to their relatively light body weights and highly developed aerobic power outputs, that the required frequency of leg movement was not optimally matched to the force necessary to produce the most economic conversion of aerobic energy into mechanical work. Thus, in competitive events their performance times were related to their maximal aerobic power output (r=–0.75) but their times were always inferior to those which one might have expected from previous aerobic power weight data collected on adult male and female athletes.     

Treadmill validation of an over-ground walking test to predict peak oxygen consumption

Summary The purpose of this study was to determine whether a test developed to predict maximal oxygen consumption (VO_2max) during over-ground walking, was similarly valid as a predictor of peak oxygen consumption (VO₂) when administered during a 1-mile (1.61 km) treadmill walk. Treadmill walk time, mean heart rate over the last 2 full min of the walk test, age, and body mass were entered into both generalized (GEN Eq.) and gender-specific (GSP Eq.) prediction equations. Overall results indicated a highly significant linear relationship between observed peakVO₂ and GEN Eq. predicted values (r=0.91), a total error (TE) of 5.26 ml · kg^–1 · min^–1 and no significant difference between observed and predicted peakVO₂ mean values. The peakVO₂ for women (n = 75) was predicted accurately by GSP Eq. (r = 0.85; TE = 4.5 ml · kg^–1 · min^–1), but was slightly overpredicted by GEN Eq. (overall mean difference = 1.4 ml · kg^–1 · min^–1;r=0.86; TE = 4.56 ml · kg^–1 · min^–1). No significant differences between observed peakVO₂ and either GEN Eq. (r=0.85; TE=4.3 ml · kg^–1 · min^–1) or GSP Eq. (r=0.85; TE = 4.8 ml · kg^–1 · min^–1)predicted values were noted for men (n=48) with peakVO₂ values less than or equal to 55 ml · kg^–1 · min^–1. However, both equations significantly underpredicted peakVO₂ for the remaining high peakVO₂ men (n = 22). In conclusion, the over-ground walking test, when administered on a treadmill, is a valid method of predicting peakVO₂ but underpredicts peakVO₂ of subjects with observed high peakVO₂ values. Present address: Human Performance Laboratory State University, Muncie, IN 47306, USA     

Supramaximal cycle tests do not detect seasonal progression in performance in groups of elite speed skaters

Summary Seven female and eight male elite junior skaters performed cycle ergometer tests at four different times during the 1987/1988 season. The tests consisted of a Wingate-type 30-s sprint test and a 2.5-min supramaximal test. The subjects were tested in February, May and September 1987 and in January 1988. Maximal oxygen consumption was measured during the 2.5-min test. With the exception of the maximal oxygen consumption of the women in May which was about 6% lower than in the other three tests, no seasonal changes in the test results could be observed —this, in spite of a distinct increase in training volume (from 10 to more than 20 h · week^–1) and training intensity in the course of the season. When the test data were compared to those of elite senior skaters, it appeared that the junior skaters showed the same values for mean power output during the sprint test [14.2 (SD 0.4) W · kg^–1 for the men and 12.6 (SD 0.5) W · kg^–1 for the women] and maximal oxygen consumption [63.1 (SD 2.8) ml· kg^–1 · min^–1 for the men and 55.3 (SD 3.5 ml · kg^–1 · min^–1 for the women, respectively] as found for senior skaters. It seemed, therefore, that the effects of training in these skaters had already levelled off in the period before they participated in this investigation. In contrast to previous studies, no relationship could be shown between the test results and skating performance. This was most likely due to the homogenous character of the groups (mean standard deviations in power and oxygen consumption were only 5%). It was concluded that the present cycle tests used to measure aerobic and anaerobic power were obviously not of use in evaluating seasonal changes in performance in these groups of highly trained athletes.     

Effect of calcium,furosemide and chlorothiazide on net volume reabsorption and basolateral membrane potential of the distal tubule

In the distal tubule of the isolated kidney of Amphiuma net volume reabsorption (split-oil droplet method) and basolateral membrane potential ( _b ) were measured. Luminal perfusion solution could be changed rapidly from 108 mmol·l^–1 NaCl plus 0.1 mmol·l^–1 calcium to solutions containing 103 or 97 mmol·l^–1 NaCl plus 3.6 or plus 7.2 mmol·l^–1 calcium. Furthermore, 10^–4 mol·l^–1 furosemide or chlorothiazide were applied luminally. (1) Addition of 7.2 mmol·l^–1 calcium hyperpolarized _b from –73.4 mV to –108.3 mV and inhibited net volume reabsorption. (2) Similarly, when furosemide was injected, _b was hyperpolarized and net volume reabsorption reduced. Application of both high calcium and furosemide further inhibited volume reabsorption. (3) The effects of chlorothiazide were similar to those of furosemide. However, when both high calcium and chlorothiazide were administered _b and volume reabsorption were almost normalized. (4) The data are consistent with the hypothesis that calcium and the diuretics interfere primarly with chloride uptake across the luminal membrane and thus reduce sodium chloride transport. When chlorothiazide in the presence of high luminal calcium almost normalized chloride transport, it is likely that its effects were by stimulating calcium transport and thus increasing intracellular calcium activity.Supported by Deutsche Forschungsgemeinschaft (Wi 328)The paper was presented, in part, at the XXVIIth Int. Congr. Physiol. Sci., Paris 1977, Proc. Vol. 13:304     

Effects of prolonged cycle ergometer exercise on maximal muscle power and oxygen uptake in humans

Summary The mechanical power (W_tot, W·kg^–1) developed during ten revolutions of all-out periods of cycle ergometer exercise (4–9 s) was measured every 5–6 min in six subjects from rest or from a baseline of constant aerobic exercise [50%–80% of maximal oxygen uptake (VO_2max)] of 20–40 min duration. The oxygen uptake [VO₂ (W·kg^–1, 1 ml O₂ = 20.9 J)] and venous blood lactate concentration ([la]_b, mM) were also measured every 15 s and 2 min, respectively. During the first all-out period, W_tot decreased linearly with the intensity of the priming exercise (W_tot = 11.9–0.25·VO₂). After the first all-out period (i greater than 5–6 min), and if the exercise intensity was less than 60% VO_2max, W_tot, VO₂ and [la]_b remained constant until the end of the exercise. For exercise intensities greater than 60% VO_2max, VO₂ and [la]_b showed continuous upward drifts and W_tot continued decreasing. Under these conditions, the rate of decrease of W_tot was linearly related to the rate of increase of V [(d W_tot/dt) (W·kg^–1·s^–1) = 5.0·10^–5 –0.20·(d VO₂/dt) (W·kg^–1·s^–1)] and this was linearly related to the rate of increase of [la]_b [(d VO₂/dt) (W·kg^–1·s^–1) = 2.310^–4 + 5.910^–5·(d [la]_b/dt) (mM·s^–1)]. These findings would suggest that the decrease of W_tot during the first all-out period was due to the decay of phosphocreatine concentration in the exercising muscles occurring at the onset of exercise and the slow drifts of VO₂ (upwards) and of W_tot (downwards) during intense exercise at constant W_tot could be attributed to the continuous accumulation of lactate in the blood (and in the working muscles).     

Effects of pre-exercise carbohydrate feedings on muscle glycogen use during exercise in well-trained runners

Summary The purpose of this study was to examine the effects of pre-exercise glucose and fructose feedings on muscle glycogen utilization during exercise in six well-trained runners ( =68.2±3.4 ml·kg^–1·min^–1). On three separate occasions, the runners performed a 30 min treadmill run at 70% . Thirty minutes prior to exercise each runner ingested 75 g of glucose (trial G), 75 g of fructose (trial F) or 150 ml of a sweetened placebo (trial C). During exercise, no differences were observed between any of the trials for oxygen uptake, heart rate or perceived exertion. Serum glucose levels were elevated as a result of the glucose feeding (P<0.05) reaching peak levels at 30 min post-feeding (7.90±0.24 mmol·l^–1). With the onset of exercise, glucose levels dropped to a low of 5.89±0.85 mmol·l^–1 at 15 min of exercise in trial G. Serum glucose levels in trials F and C averaged 6.21±0.31 mmol·l^–1 and 5.95±0.23 mmol·l^–1 respectively, and were not significantly different (P<0.05). There were also no differences in serum glucose levels between any of the trials at 15 and 30 min of exercise. Muscle glycogen utilization in the first 15 min of exercise was similar in trial C (18.8±8.3 mmol·kg^–1), trial F (16.3±3.8 mmol·kg^–1) and trial G (17.0±1.8 mmol·kg^–1), and total glycogen use was also similar in trial C (25.6±7.9 mmol·kg^–1), trial F (35.4±5.7 mmol·kg^–1) and trial G (24.6±3.2 mmol·kg^–1). In contrast to previous research, these results suggest that pre-exercise feedings of fructose or glucose do not affect the rate of muscle glycogen utilization during 30 min of treadmill running in trained runners.     

Sodium citrate and anaerobic performance: implications of dosage

Summary The use of sodium bicarbonate to improve anaerobic performance is well known but other buffering agents have been used with some success. Sodium citrate is one such substance which has been used but without the normal gastro-intestinal discomfort usually associated with sodium bicarbonate ingestion. The effects of five doses of sodium citrate (0.1 g·kg^–1 body mass, 0.2 g·kg^–1 body mass, 0.3 g·kg^–1 body mass, 0.4 g·kg^–1 body mass and 0.5 g·kg^–1 body mass) on anaerobic performance were studied in order to determine the minimal and most productive dose required for performance enhancement. A maximal test was performed for 1^–1, min on a cycle ergometer. Total work and peak power were measured at the end of the exercise period. Blood was drawn 1.5 h prior to the test session and measured for pH, partial pressure of carbon dioxide and concentrations of bicarbonate, base excess and lactate. In all but the control and placebo trials subjects then ingested one of five doses of sodium citrate which was contained in 400 ml of flavoured drink. Blood was again taken 90 min later and this was repeated after the completion of the exercise test. The greatest amount of work was completed in the trial with citrate given at 0.5 g·kg^–1 body mass (44.63 kJ, SD 1.5) and this was also true for peak power (1306 W, SD 75). The post-exercise blood lactate concentration was also highest during this trial 15.9 mmol·1^–1, SD 1.1. Post-exercise pH decreased significantly in all trials (P<0.0001) while the administration of the sodium citrate in all doses above 0.1 g·kg^–1 body mass significantly increased resting pH values. Blood bicarbonate concentrations also increased with dose in an almost linear fashion with the administration of sodium citrate. Bicarbonate increases were all significant, P<0.05 (citrate 0.1 g·kg^–1 body mass), P<0.01 (citrate 0.2 g·kg^–1 body mass, 0.3 g·kg^–1 body mass and 0.4 g·kg^–1 body mass) and P<0.005 (citrate 0.5 g·kg^–1 body mass). The administration of sodium citrate also significantly increased base excess values (citrate 0.1 g·kg^–1 body mass,P<0.01; 0.2 g·kg^–1body mass, P<0.001; 0.3 g·kg^–1 body mass, P<0.001; 0.4 g·kg^–1 body mass, P<0.001; 0.5 g·kg^–1 body mass, P<0.0001) above control and placebo values. All post-exercise base excess values were significantly lower than basal or pre-exercise values (P<0.0001). It was concluded that sodium citrate was an effective ergogenic aid for anaerobic performance of approximately 60-s duration, with the most effective of those dosages tested being 0.5 g·kg^–1 body mass.     

Effects of moderate external loading on the aerobic demand of submaximal running in men and 10 year-old boys

Summary The effects of moderate external loading on the aerobic demand of submaximal running were studied in habitually active adult men (29–37 yrs) and 10 year-old boys. The load was symmetrically placed around the trunk and adjusted to correspond to 10% of body weight. Running was performed on a treadmill at 8, 10 and 11 km · h^–1 (2.2, 2.8 and 3.1 m · s^–1). A small, but consistent decrease in net oxygen uptake (gross oxygen uptake in ml · kg^–1 · min^–1 minus calculated basal metabolic rate) with load was observed in both groups at all speeds, except for the men at 8 km · h^–1. The decrease was larger for the boys and tended to enhance with speed. The boys had a higher net oxygen uptake than the adults at all unladen running velocities, whereas the difference in the loaded condition was significant only at the highest speed. The decrease in net oxygen uptake with load could not be directly correlated with differences in body weight or step frequency. It is hypothesized that a difference in the utilization of muscle elastic energy could underlie part of the age and load dependent changes observed in running economy.     

Blood volume changes and arginine vasotocin (AVT) blood concentration in conscious fresh water and salt water adapted ducks

Blood volume changes consisting in the removal and reinfusion respectively, of 10% of the estimated blood volume (23.2 ml on average) were induced to determine their effects on the blood concentration of arginine vasotocin (AVT), the antidiuretic hormone (ADH) of birds, in fresh water adapted ducks (water ducks) with blood osmolalities and ADH concentrations similar to those of normally hydrated mammals, and in salt water adapted ducks (salt ducks) with chronically elevated blood osmolalities and ADH concentrations. The investigations were carried out in steady state conditions, when infusion of 1 ml·min^–1 of isotonic saline was matched by the excretion in water ducks and when infusion of 0.4 ml·min^–1 of 1,000 mosmolal saline was matched by the salt gland excretion in the salt ducks.After blood removal, AVT blood concentration (mean ±SE) increased from 6.5±0.4 to 8.4±0.6 pg·ml^–1 in water ducks and from 18.1±1.6 to 22.6±1.9 pg·ml^–1 in salt ducks. The respective blood osmolalities of 297.4±1.4 and 318.6±3.3 mOsm·kg^–1 did not change. Reinfusion of the blood after steady-state conditions had been reattained decreased blood AVT from 7.9±0.7 to 6.7±0.5 pg·ml^–1 in water ducks. In the salt ducks AVT concentration had already returned to the control level before blood reinfusion which induced no further reduction. The blood osmolalities remained unchanged in both groups.During blood removal and reinfusion, the excretion rate of the kidneys in water ducks and the salt glands in salt ducks were temporarily reduced and enhanced respectively, the effect being not symmetrical for salt gland secretion.For water ducks, the volume sensitivity of AVT release was found comparable to that of mammals, when related to the induced blood volume changes, the responses to blood removal and reinfusion being approximately equal in absolute terms. In the salt ducks, the volume sensitivity of AVT release was clearly expressed during blood removal but insignificant during blood reinfusion.Supported by the Alexander v. Humboldt-StiftungSupported by the Deutsche Forschungsgemeinschaft     

Model of bicarbonate secretion by resting frog stomach fundus mucosa I. Transepithelial measurements

In the present in vitro experiments on gastric fundus mucosa of Rana esculenta we try to define the mechanism of alkaline secretion that is observed in summer frogs in the resting stomach (blockage of HCl secretion by ranitidine, 10^–5 mol/l). The transepithelial voltage and the rate of alkalinization (ASR) of an unbuffered gastric lumen perfusate was measured as a function of serosal (and mucosal) fluid composition. ASR was high (0.88±S.E. 0.09 Eq·cm^–2·h^–1, n=11) during serosal bath perfusion with HCO₃ ^–-Ringer solution, decreased slightly to 0.50±0.07 Eq·cm^–2·h^–1 (n=6) in HCO₃ ^–-free HEPES-buffered Ringer solution of the same pH, and decreased to approximately 20% when carbonic anhydrase was inhibited by acetazolamide. While replacement of mucosal or serosal Cl^– did not — within 1 h — significantly alter ASR, replacement of serosal Na⁺ in the presence or absence of HCO₃ ^– strongly reduced ASR, and a similar reduction was observed after serosal application of the anion transport inhibitor DIDS (4,4-diisomiocyanatostilbene-2,2-disulphonate, 2·10^–4 mol/l), the metabolic poison rotenone (10^–5 mol/l), the uncoupler dinitrophenol (10^–4 mol/l), and the Na⁺ pump inhibitor ouabain (10^–4 mol/l), while serosal amiloride (10^–4 mol/l) had no effect. These data can be accounted for by a model of alkaline secretion that consists of basolateral HCO₃ ^– uptake from the serosal fluid into the cell via a DIDS-inhibitable Na⁺(HCO₃ ^–)_n-cotransporter and HCO₃ ^– secretion from the cell to the gastric lumen via an anionic conductance pathway. Microelectrode experiments on oxyntopeptic cells reported in the subsequent paper suggest that these cells may also be involved in the resting state alkaline secretion.     

Influence of aldosterone on epithelial leakiness of rat proximal tubules

Oil blocked superficial segments of late proximal tubules were perfused with salt free isosmolal mannitol solution. Time course of total net ion influx into the lumen after sudden stop of perfusion was monitored by continuous measurement of the conductivity of tubular fluid inside the lumen. Double barreled microelectrodes with high coupling resistance (R _c=350–450 kOhm) were used as microconductivity probes. The observed time course was interpreted in terms of a two compartment system. Time constants for equilibration were 5.9±2.8 (SD) s in control rats, 14.4±8.0 s in adrenalectomized rats and 5.5±2.3 s in adrenalectomized rats substituted with 100 g·kg^–1 · d^–1 aldosterone for 3 days. The observed effect of aldosterone on the equilibration time constant indicates that this hormone increases the leakiness of proximal tubular epithelium for passive ion influx into the lumen.Supported by Deutsche Forschungsgemeinschaft (Wi 328/6)